1. Field of Invention
The present invention relates to an image forming apparatus which discharges a paper after turning the paper over and which is capable of forming images on both sides of a paper, as desired. More particularly, the present invention relates to an image forming apparatus including a paper positioning device for positioning a paper being conveyed in the apparatus.
2. Description of Related Art
Generally, an image forming apparatus which can print on both sides of a paper is selectively operable in the following three different modes. In a first mode, the apparatus directly discharges a paper having an image printed on one side thereof, in an orientation in which the printed image faces upwardly. This mode is hereinafter referred to as "the usual mode." In a second mode, the apparatus turns over the paper having an image printed on one side thereof via a turning mechanism and then discharges the paper such that the printed image on the first side is face down. This mode is hereinafter referred to as "the turn-over mode." In a third mode, the apparatus delivers the paper having a printed image on one side thereof from the turning mechanism to a two sided-printing mechanism or duplex mechanism and then feeds the paper again to an image forming section for forming an image on the other side of the paper. This mode is hereinafter referred to as "the duplex mode."
In the turn-over mode and the duplex mode, the paper having an image printed on one side thereof is apt to skew when the paper is turned over. It is a common practice with the above apparatus to use a paper positioning device for positioning the paper such that the paper does not skew before or after it is turned over, as disclosed in Japanese Patent Laid-Open Publication No. 7-206224 by way of example.
The problem with the conventional paper positioning device is that it requires a great number of mechanical parts which must be assembled together and cooperate to achieve the desired result. In addition, the conventional paper positioning device involves play or positional deviation caused by an inaccuracy in the size and position of the various mechanical parts making up the paper positioning device, as well as, changes caused by thermal expansion of such parts. The positional deviation or play prevents the paper positioning device from reliably and completely regulating the position of a paper and therefore, from accurately correcting the skew of the paper.
Other such devices relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No. 7-304544.